The present invention relates to a vehicle front-view monitoring system having a function of taking fail-safe measures against images irregularly monitored due to sunlight interfering.
The vehicle front-view monitoring system having CCD cameras has recently attracted much attention. The system recognizes driving conditions such as a distance to a vehicle travelling ahead based on images taken by the cameras and warns a driver of danger or controls the vehicle such as by downshifts.
Recognition of the driving conditions using a stereo-distance measuring technique obtains a positional difference (parallax) on an object in a pair of the images and calculates the distance to the vehicle travelling ahead by trigonometrical survey.
Such a vehicle front-view monitoring system requires fail-safe measures for insuring safe driving. A failure to be detected by the system is a fault monitoring condition such as when the vehicle in front is beyond recognition while monitoring cameras are facing weak sunlight.
Image monitoring failures are discussed with reference to FIGS. 1 to 3.
When monitoring vehicles that are traveling ahead (FIG. 1) while facing weak sunlight, disc-like diffusion patterns could appear on the monitored image, as illustrated on the left-upper side in FIG. 2, due to saturation of luminance. Such a disc-like diffusion pattern appearing on the monitored image while the vehicle is facing the sunlight is called a sunlight-diffusion disc hereinafter. These sunlight-diffusion discs cause the saturation of pixel luminance on the disc areas and the surrounding areas. A correct image data therefore can not be obtained, or vehicles in front are masked by the sunlight-diffusion discs, which results
FIG. 3 illustrates distance-data calculation based on stereo images (a reference image and an image to be compared such as shown in FIG. 1).
In FIG. 3, black sections have a big luminance change between the adjacent pixels in the horizontal direction. These sections carry distance data (depth). The intensities of most pixels in the sunlight-diffusion disc area have been saturated, so that no distance data is calculated in this area (a lost state). Moreover, the disc edges have a big luminance change in the horizontal direction, so that the incorrect distance data could be calculated.
Insuring safe driving in such a fault condition due to a generation of the sunlight-diffusion discs discussed above requires the fail-safe measures to temporarily halt the monitoring function.